AudioMulch

In this article Keiran says, "I really like Audiomulch, it's one on my favourite bits of software. It's so stripped-down, and you can really abuse it. Reason just makes trance music, and you're not really allowed to piss around with it too much and everything's got this horrible reverbed sound, and I kind of hate it — Audiomulch is my preferred version of that idea(...)"

Gregg Gillis has used Audiomulch since 2000 for the Girl Talk Project
AudioMulch is software for live performance, audio processing,
sound design and music composition.
Girl Talk uses it both for performing live and creating his albums.
He also speaks about how he uses it in this Rolling Stone interview:
https://www.youtube.com/watch?v=NS921BrPiH0